Overclocking

AMD positions their FX processors as overclocking-friendly solutions. They are all marked as “Black Edition” units and have unlocked multipliers, which makes overclocking very simple. In fact, it is their only indisputable advantage over IntelSandyBridge. Among Intel’s products, only three LGA 1155 CPUs from the K-series overclock fully and they are priced at over $200. It means that in the sub-$200 price range computer enthusiasts can only go with AMD, primarily FX series CPUs. So, it is FX-6100 or FX-4100 that will most likely become an optimal overclocking choice.

Since we had the entire lineup of currently available AMD FX processors at our disposal, we decided to check out the overclocking potential of all four models. Note that we didn’t aim for setting an overclocking record. Our goal was different: to determine the frequency, at which desktop Bulldozer processors will be able to work stably and fault-free in 24/7 mode. Therefore, we only increased the processor core voltage by 0.1-0.15 V and used NZXT Havik 140 air-cooler for proper processor cooling. We tested the system stability during overclocking in LinX 0.6.4 64 bit utility.

We managed to increase the clock frequency of our quad-core AMD FX-4100 processor to 4.6 GHz without any stability issues. At the same time the NorthBridge built into it got overclocked to 2.6 GHz. The processor Vcore was only increased by 0.1 V in this case, because our particular CPU had pretty high nominal Vcore to begin with.

Six-core AMD FX-6100 processor revealed a slightly lower overclocking potential. Even though we raised its core voltage by 0.15 V, the highest we could go on the frequency was 4.4 GHz. As for the NorthBridge built into the processor, it practically didn’t get overclocked at all: we managed to increase its frequency only by 200 MHz above the nominal – to 2.2 GHz.

The junior eight-core desktop Bulldozer processor, FX-8120, got easily overclocked to 4.5 GHz. It required 0.15 V Vcore increase to ensure stability, just like in the previous case. At the same time we managed to increase to 2.6 GHz the frequency of the NorthBridge integrated into the CPU.

We already overclocked AMD FX-8150 processor before in our previous Bulldozer review. Back then it proved capable of working at 4.6 GHz frequency. Our today’s test session confirmed the previously obtained result. With the core voltage increased by 0.15 V above the nominal this processor remained perfectly stable at the attained frequency, with the NorthBridge sped up to 2.4 GHz at the same time.

Overall, all desktop processors with Bulldozer microarchitecture demonstrated pretty similar overclocking potential. All of them could be easily overclocked to 4.4-4.6 GHz and remain stable at these speeds over a long period of time. The operational temperature of the processor cores remain within acceptable range, and do not exceed 60-65°C even for the eight-core FX CPUs with 125 W TDP.

Although these results are quite encouraging, the experiments with overclocked AMD FX processors left a very ambiguous impression. We hoped that we would be able to turn junior Bulldozer processors with reduced number of computational cores into eight-core ones by somehow unlocking the disabled cores, but to our regret AMD made it absolutely impossible, even though this function was a signature feature of all previous-generation CPUs. Therefore, the only way computer enthusiasts will be able to boost the performance of the new FX processors is by raising their clock speed.

In order to estimate the performance gain from AMD FX overclocking, we tested all four processors at the nominal and overclocked frequencies. The obtained results were then compared against the performance of Core i5-2500K in nominal mode and at 4.6 GHz frequency, which may be considered typical overclocking for this particular CPU.

The highest performance gain results from overclocking the junior eight-core FX-8120 model. It is, in fact, quite logical, because its original clock frequency is the lowest in the entire family. However, you will notice a substantial performance improvement after overclocking any of the Bulldozer CPUs. You can count on an average 25% increase above the nominal, which is about the gain you would get from overclocking Intel’s Sandy Bridge CPUs with an unlocked clock frequency multiplier.

However, FX processors really suffer from their originally low performance. Even overclocked eight-core Bulldozer CPUs can’t always catch up in performance with a Core i5-2500K working at its nominal frequencies. And if we compare all processors in overclocked mode, the only obvious argument in favor of the AMD products for overclocking needs will be their lower price.